Browsing by Author "Liang, Chen-Wei"

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Atomic-Scale Evolution of Local Electronic Structure Across Multiferroic Domain Walls
(2011-04-05)
Chiu, Ya-Ping
;
Chen, Yu-Ting
;
Huang, Bo-Chao
;
Shih, Min-Chuan
;
Yang, Jan-Chi
Direct evidence of the electronic configurations across domain walls in BiFeO(3) is quantitatively characterized by cross-sectional scanning tunneling microscopy. Atomic-scale band evolution and the asymmetrically built-in potential barrier at domain boundaries are demonstrated. The 109 degrees domain walls register a remarkable decrease in the bandgap, suggesting a new route to control the local conducting channels within 2 nm.
Direct spectroscopic evidence of charge reversal at the Pb(Zr(0.2)Ti(0.8))O(3)/La(0.7)Sr(0.3)MnO(3) heterointerface
(2011-01-21)
Wu, Chung-Lin
;
Lee, Pei-Wei
;
Chen, Yi-Chun
;
Chang, Lo-Yueh
;
Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr(0.2)Ti(0.8))O(3) (PZT) ultrathin film and a bottom La(0.7)Sr(0.3)MnO(3) (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
Direct spectroscopic evidence of charge reversal at the Pb(Zr0.2Ti0.8)O-3/La0.7Sr0.3MnO3 heterointerface
(2011-01-21)
Wu, Chung-Lin
;
Lee, Pei-Wei
;
Chen, Yi-Chun
;
Chang, Lo-Yueh
;
Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr0.2Ti0.8)O-3 (PZT) ultrathin film and a bottom La0.7Sr0.3MnO3 (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
Epitaxial Photostriction-Magnetostriction Coupled Self-Assembled Nanostructures
(2012-08-01)
Liu, Heng-Jui
;
Chen, Long-Yi
;
He, Qing
;
Liang, Chen-Wei
;
Chen, Yu-Ze
Self-assembled vertical nanostructures take advantage of high interface-to-volume ratio and can be used to design new functionalities by the choice of a proper combination of constituents. However, most of the studies to date have emphasized the functional controllability of the nanostructures using external electric or magnetic fields. In this study, to introduce light (or photons) as an external control parameter in a self-assembled nanostructure system, we have successfully synthesized oxide nanostructures with CoFe2O4 nanopillars embedded in a SrRuO3 matrix. The combination of photostrictive SrRuO3 and magnetostrictive CoFe2O4 in the intimately assembled nanostructures leads to a light-induced, ultrafast change in magnetization of the CoFe2O4 nanopillars. Our work demonstrates a novel concept on oxide nanostructure design and opens an alternative pathway for the explorations of diverse functionalities in heteroepitaxial self-assembled oxide nanostructures.
Local Conduction at the BiFeO3-CoFe2O4 Tubular Oxide Interface
(1970-01-01)
Hsieh, Ying-Hui
;
Liou, Jia-Ming
;
Huang, Bo-Chao
;
Liang, Chen-Wei
;
He, Qing
"In strongly correlated oxides, heterointerfaces, manipulating the interaction, frustration, and discontinuity of lattice, charge, orbital, and spin degrees of freedom, generate new possibilities for next generation devices. In this study, existing oxide heterostructures are examined and local conduction at the BiFeO3-CoFe2O4 vertical interface is found. In such heteronanostructures the interface cannot only be the medium for the coupling between phases, but also a new state of the matter. This study demonstrates a novel concept on for oxide interface design and opens an alternative pathway for the exploration of diverse functionalities in complex oxide interfaces."
Misorientation Control and Functionality Design of Nanopillars in Self-Assembled Perovskite-Spinel Heteroepitaxial Nanostructures
(2011-05-01)
Liao, Sheng-Chieh
;
Tsai, Pei-Yu
;
Liang, Chen-Wei
;
Liu, Heng-Jui
;
Yang, Jan-Chi
In this study, advanced control of crystallographic orientations and magnetic properties of self-assembled nanostructures via rational selections of substrates is demonstrated. We show that in the perovskite spinel BiFeO(3)-CoFe(2)O(4) model system the crystal orientation of self-assembled CoFe(2)O(4) nanopillars can be tuned among (001), (011), and (111), while that of the BiFeO(3) matrix is fixed in (001). Moreover, the resultant CoFe(2)O(4) nanopIllars appear in various shapes: pyramid, roof, and triangular platform, respectively. The tunable nanostructures through this approach enable the control of material functionality such as the magnetic anisotropy of CoFe(2)O(4). This study opens a new pathway for the engineering of self-assembled heteroepitaxial nanostructures.
Nanoscale Structure and Mechanism for Enhanced Electromechanical Response of Highly Strained BiFeO(3) Thin Films
(2011-07-26)
Damodaran, Anoop R.
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Liang, Chen-Wei
;
He, Qing
;
Peng, Chun-Yen
;
Chang, Li
The presence of a variety of structural variants in BiFeO(3) thin films give rise to exotic electric-field-induced responses and resulting electromechanical responses as large as 5%. Using high-resolution X-ray diffraction and scanning-probe-microscopy-based studies the numerous phases present at the phase boundaries are identified and an intermediate monoclinic phase, in addition to the previously observed rhombohedral- and tetragonal-like phases, is discovered.
Nanoscale Structure and Mechanism for Enhanced Electromechanical Response of Highly Strained BiFeO3 Thin Films
(2011-07-26)
Damodaran, Anoop R.
;
Liang, Chen-Wei
;
He, Qing
;
Peng, Chun-Yen
;
Chang, Li
The presence of a variety of structural variants in BiFeO3 thin films give rise to exotic electric-field-induced responses and resulting electromechanical responses as large as 5%. Using high-resolution X-ray diffraction and scanning-probe-microscopy-based studies the numerous phases present at the phase boundaries are identified and an intermediate monoclinic phase, in addition to the previously observed rhombohedral- and tetragonal-like phases, is discovered.
Strain-driven phase boundaries in BiFeO(3) thin films studied by atomic force microscopy and x-ray diffraction
(2012-01-17)
Liu, Heng-Jui
;
Liang, Chen-Wei
;
Liang, Wen-I
;
Chen, Hsiang-Jung
;
Yang, Jan-Chi
We report a detailed study on the strain-driven phase transition between the tetragonal-like and rhombohedral-like phases in epitaxial BiFeO(3) (BFO) thin films which focuses on their structural nature, thermodynamic stability, and ferroelectric/piezoelectric properties. We first show that the tetragonal-like phase, which has a large c/a ratio (similar to 1.2), in the compressively strained BFO is thermodynamically more favorable at high temperature and high strain state (small thickness). We also report a phase transition between two monoclinic phases at 150 degrees C. The two monoclinic phases are differentiated by their c-axis parameters and tilting angles: The low-temperature phase (M(C)) has a c-axis parameter of 4.64 angstrom and a tilting angle (beta = 88.5 degrees) along the a axis, while the high-temperature phase (M(A)) has a c-axis parameter of 4.66 angstrom and a tilting angle (beta = 86.8 degrees) along both of the a and b axes. We further show that samples undergoing the M(C)-M(A) phase transition exhibit ferroelectric polarization rotation and piezoelectric enhancement. Our findings directly unveil the close links between structural changes, polarization rotation, and large piezoelectricity at morphotropic phase boundaries in BiFeO(3).
Strain-driven phase boundaries in BiFeO3 thin films studied by atomic force microscopy and x-ray diffraction
(2012-01-17)
Liu, Heng-Jui
;
Liang, Chen-Wei
;
Liang, Wen-I
;
Chen, Hsiang-Jung
;
Yang, Jan-Chi
We report a detailed study on the strain-driven phase transition between the tetragonal-like and rhombohedral-like phases in epitaxial BiFeO3 (BFO) thin films which focuses on their structural nature, thermodynamic stability, and ferroelectric/piezoelectric properties. We first show that the tetragonal-like phase, which has a large c/a ratio (similar to 1.2), in the compressively strained BFO is thermodynamically more favorable at high temperature and high strain state (small thickness). We also report a phase transition between two monoclinic phases at 150 degrees C. The two monoclinic phases are differentiated by their c-axis parameters and tilting angles: The low-temperature phase (M-C) has a c-axis parameter of 4.64 angstrom and a tilting angle (beta = 88.5 degrees) along the a axis, while the high-temperature phase (M-A) has a c-axis parameter of 4.66 angstrom and a tilting angle (beta = 86.8 degrees) along both of the a and b axes. We further show that samples undergoing the M-C-M-A phase transition exhibit ferroelectric polarization rotation and piezoelectric enhancement. Our findings directly unveil the close links between structural changes, polarization rotation, and large piezoelectricity at morphotropic phase boundaries in BiFeO3.
Structural study in highly compressed BiFeO3 epitaxial thin films on YAlO3
(2012-09-01)
Liu, Heng-Jui
;
Chen, Hsiang-Jung
;
Liang, Wen-I
;
Liang, Chen-Wei
;
Lee, Hsin-Yi
We report a study on the thermodynamic stability and structure analysis of the epitaxial BiFeO3 (BFO) thin films grown on YAlO3 (YAO) substrate. First, we observe a phase transition of M-C-M-A-T occurs in thin sample (<60 nm) with an utter tetragonal-like phase (denoted as M-II here) with a large c/a ratio (similar to 1.23). Specifically, MII phase transition process refers to the structural evolution from a monoclinic M-C structure at room temperature to a monoclinic M-A at higher temperature (150 degrees C) and eventually to a presence of nearly tetragonal structure above 275 degrees C. This phase transition is further confirmed by the piezoforce microscopy measurement, which shows the rotation of polarization axis during the phase transition. A systematic study on structural evolution with thickness to elucidate the impact of strain state is performed. We note that the YAO substrate can serve as a felicitous base for growing T-like BFO because this phase stably exists in very thick film. Thick BFO films grown on YAO substrate exhibit a typical "morphotropic-phase-boundary"-like feature with coexisting multiple phases (M-II, M-I, and R) and a periodic stripe-like topography. A discrepancy of arrayed stripe morphology in different direction on YAO substrate due to the anisotropic strain suggests a possibility to tune the MPB-like region. Our study provides more insights to understand the strain mediated phase co-existence in multiferroic BFO system. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746036]